I like testcases. One testcase results in more understanding than ten page article or weeks of data collection. This is why we need reproducible testcases if we want to explore mutex contention. Testcases will also give me a possibility to demonstrate how to use mutex contention diagnostics tools embedded in Oracle. I will use Oracle 188.8.131.52 for Linux X86 32bit on my Dual-Core laptop in this posts. Your numbers for other Oracle versions and platforms may vary.
I. “Cursor: pin S” contention testcase:
Each time the session execute SQL operator, it needs to ‘pin’ the cursor in library cache using mutex. True mutex contention arises when the same SQL operator executes concurrently at high frequency. Therefore the simplest testcase for “Cursor: pin S” contention should look like:
begin for i in 1..1000000 loop execute immediate 'select 1 from dual where 1=2'; end loop; end; /